1. Technical Field
The embodiments herein generally relate to a transport network and particularly relates to telecommunication information transportation. The embodiments herein more particularly relates to preventing holding-off of a protection switching for a plurality of alarms at a client layer in a nested protection system.
2. Description of the Related Art
Network protection is an essential requirement in transport networks as such networks are quite susceptible to faults. As it cannot be assumed that the end-to-end link is always available, some form of traffic protection is required via a backup link to provide end-to-end connectivity. Generally in any protection mechanism, there are M protect entities which protect N work entities hence forming a M:N protection group. In case a protect entity is not required for protection, it can carry a low priority pre-emptible extra traffic.
the protection mechanism basically includes a signaling protocol, a protection controller and a switch matrix. A signaling protocol coordinates between the transmitting ends and the receiving ends so as to avoid any misconnection and also to synchronize the activity of each ends, in transport networks this is generally achieved through Kbytes. The protection controller takes decisions with respect to switching/bridging/squelching and the like of the traffic via the signaling; protocol for the coordination and also instructs the switch matrix to route the traffic from work or protect.
Generally, a transport network is structured as different layers with server and client relationship between the layers. A plurality of client entities is contained b a server entity, in a network many kinds of faults can occur at an entity side. The faults can be due to defects at entity's own layer or due to server layer defects such as server signal fail (SSF) and server signal degrade (SSD). An alarm filter at a particular layer takes a large number of alarms as input and maps them to some lesser number of classes (like fail or degrade) at its output. Such a compression is required as a protection controller understands only signal fail and signal degrade on its monitored entities. Even in signaling during protection switching, the only failure requests which are signaled as per the protocol are signal fail and signal degrade.
To prevent multiple protection switches and the associated oscillation of traffic from work to protect to work, the alarms or faults being fed directly to the protection controller are soaked for a specified period of time (called a hold-off period). After the hold-off period has expired, the failure is re-evaluated and is then fed to the protection controller. Typical cases when hold-off is being configured are holding of defects at respective layer due to an upstream protection mechanism already available in the network or holding of server layer signals, server signal fail (SSF) and server signal degrade (SSD) in nested protection configurations.
Nested protection is a configuration in which there is a protection configuration available at both the server entity and the respective client entity at the same time. One of the well known examples of nested protection configuration in prior art is ITU-T G.842 compliant MSSP Ring Dual Node Interconnection (DNI) and Bellcore GR.1230 compliant Dual Transmit Method for ring interconnections for a BLSR configuration in the network. If a protection group is configured on a server entity, it is possible that due to some triggers to the SLPC (Serer layer protection controller), the SLPC needs to squelch some of the clients contained inside the server layer. This is done by asserting AIS (all ones signal) on the respective clients. Squelching is done by the protection controller primarily to avoid misconnection in the traffic mainly in two scenarios, one when extra traffic is dropped on the protect in any of the protection configurations be it MSP or MSSP Ring or SNCP and the other during ring segmentation or node isolation in case of MSSP Ring. These protection configurations are well known in the prior art as per ITU-T G.841 standard. Now, due to this the specific squelch signal gets categorized into AIS and hence, the hold-off mechanism ends up holding, off this alarm unnecessarily. Further, if the SLPC needs to squelch the client signal, the CLPC (Client Level Protection Controller) cannot take any corrective switching action on that until the hold-off time expires. As the typical hold-off values are in steps of 100 ms, so the hold-off period can range from 100 ms, 200 ms to 10 seconds or more. This means that the traffic outage time can be significant while it could have been possible to rectify the outage due to some protection mechanism available on the client layer itself. As there is no distinction between an AIS generated due to squelching and an AIS due to other faults in the network the AIS due to squelch gets held-off unnecessarily if hold-off is configured which leads to a delay in protection switching action by the client layer protection controller.
In view of the foregoing, there exists a need to provide a method and system for protection switching which does not hold off the AIS due to squelching. There also exists a need to provide a method and system which enables the client layer protection controller to take corrective actions to protect traffic at the client layer.
The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.